1. Field of the Invention
The present invention relates to a cooling device for cooling the inside of a case holding cooled elements.
2. Description of the Related Art
There are many examples in may industrial fields of cases for holding cooled elements to which the present invention can be applied. In the present invention, however, in order to facilitate the understanding, a communication device in the field of electronics, especially the field of information communication, will be explained as a preferred example of such a case.
A communication device is generally constituted by a large number of integrated circuits (ICs) and large scale integrated circuits (LSIs) mounted on a substrate and surrounded by a case. These ICs and LSIs have been increased in density in recent years and further have been given higher functions and therefore have become much larger in power consumption. Accordingly, naturally the amount of heat generated in the case forming the communication device becomes enormous. It becomes necessary to efficiently dissipate this generated heat from the case.
However, along with the increasingly sophisticated functions of the communication devices explained above, the operating frequency of the electronic circuits have become higher and have reached the GHz order. Here, so-called electromagnetic compatibility (EMC) countermeasures have becomes necessary, therefore a complete shield structure is required for the cases. However, such a shield structure makes it further difficult to efficiently dissipate the enormous generated heat from the case.
Thus, a cooling device for efficiently cooling a large number of cooled elements (ICs, LSIs, etc.) accommodated in a case has become indispensable particularly for communication devices in recent years.
Further, in recent years, due to the rapid spread of the Internet, communication devices used by for example carriers have increasing used cases provided with Ethernet® ports as interfaces. Specifically, for example, a large number of RJ-45/SFP (small form-factor pluggable) modules are being mounted as interfaces on particularly the front surfaces of communication devices.
However, in communication devices in carriers etc. mounting such RJ-45/SFP modules on the front surface of the cases, as will be explained later by using FIG. 20, special care is required.
Note that as a known art related to the present invention, there is Japanese Patent Publication (A) No. 4-252098. However, this known art does not suggest the technical idea of “employment of an air duct” characterizing the present invention and explained later.
In communication devices having ports for the above RJ-45/SFP modules etc. as a large number of interfaces on the front surface of the cases, usually intakes port are provided at the same front surfaces. For this reason, the areas which can be allotted to the intake ports on the front surfaces become much smaller. In addition, in for example communications device used by carriers described above, a plurality of the same communication devices are stacked in standard sized racks in multiple stages, therefore the heights which can be given to individual communication devices, that is, the heights of the front surface portions, are naturally restricted. In the final analysis, it is almost impossible to further increase the areas which can be allotted to the intake ports for increasing the cooling capability.
In addition, in a communication device described above, a temperature within a range of from for example 0° C. to 110° C. can be guaranteed for electrical system parts such as ICs and LSIs arranged inside the case, but only a temperature within a relatively narrow range of from for example 0° C. to 75° C. can be guaranteed for the RJ-45/SFP modules arranged on the front surface of the case. This is because these modules are optical interfaces for opto/electric conversion and electro/optic conversion including elements with extremely easily changing temperature-wavelength characteristics. For this reason, a higher cooling capability is required for the front surface side (optical interface module) more than the inside (electrical system parts) of the case. In a conventional cooling device, however, the above problem has not yet been solved due to the restriction of the height of the front surface explained above.